Interleukin 11 (“IL-11”) is a pleiotropic cytokine that stimulates a variety of hematopoietic and immune functions, such as primitive lymphohematopoietic progenitor cells and other hematopoietic growth factors which stimulate the proliferation and maturation of megakaryocytes. IL-11 is described in detail in International Application PCT/US90/06803, published May 30, 1991, as well as in U.S. Pat. No. 5,215,895; issued Jun. 1, 1993. A cloned human IL-11 was previously deposited with the American Type Culture Collection (ATCC), 10801 University Blvd., Manassas, Va., on Mar. 30, 1990 under ATCC No. 68284. Moreover, as described in U.S. Pat. No. 5,270,181, issued Dec. 14, 1993, and U.S. Pat. No. 5,292,646, issued Mar. 8, 1994, IL-11 may also be produced recombinantly as a fusion protein with another protein.
It is desirable to have concentrated forms of bulk protein, e.g. IL-11, which, in turn, may be stored and which are suitable for further manufacture of finished dosage forms of protein. Typically, a purification process for a protein results in purified, concentrated protein. This concentrated protein, also known as bulk protein, may be in a formulation buffer. Bulk protein, typically at a concentration of about 0.1 to at least 20 mg/ml, can then be shipped frozen to a fill/finish facility where it is diluted to an appropriate concentration and filled into vials. These diluted samples can be lyophilized, i.e., freeze-dried. The lyophilized samples may be kept in long-term storage and reconstituted at a later time by adding a suitable administration diluent just prior to patient use.
Protein stability can be affected inter alia by such factors as ionic strength, pH, temperature, repeated cycles of freeze/thaw and exposures to shear forces. Active protein may be lost as a result of physical instabilities, including denaturation and aggregation (both soluble and insoluble aggregate formation), as well as chemical instabilities, including, for example, hydrolysis, deamidation and oxidation, to name just a few. For a general review of stability of protein pharmaceuticals, see, for example, Manning, et al., Pharmaceutical Research 6:903–918 (1989).
While the possible occurrence of protein instabilities is widely appreciated, it is impossible to predict particular instability problems of a particular protein. Any of these instabilities can result in the formation of a protein, protein by-product, or derivative having lowered activity, increased toxicity, and/or increased immunogenicity. Also, IL-11 has a tendency to form soluble high molecular weight aggregates which can interfere with product quality and effectiveness in use. Thus, the safety and efficacy of any pharmaceutical formulation of a protein is dependent upon its stability.
In addition to stability considerations, one generally selects excipients which are or will meet with the approval of various world-wide medical regulatory agencies. The solution should be isotonic and the pH in a physiologically suitable range. The choice and amount of buffer used is important to achieve and maintain the desired pH range.
Ideally, formulations should also be stable for IL-11 bulk storage in high concentration (≧20 mg/ml, for example) which allows for relatively small volumes for fill/finish at the appropriate dose and also allows for alternate methods of administration which may require high protein concentration, e.g., sub cutaneous administration. Accordingly, there continues to exist a need in the art for methods for monitoring IL-11 protein stability (and maintaining activity levels) during the concentration process and the lyophilization process, as well as providing stable formulations during prolonged storage.